I. Field of the Invention
The present invention relates to a reinforced laminated materials of mainly vegetable fibers or lignocellulosic stalks of sorghum, corn, and sugar cane and the like and a method for the preparation of the laminated material. In particular, it concerns a laminated material used as building materials, furniture materials, heat insulating materials, sound absorbing materials, display materials, and materials for handicrafts.
II. Description of the Related Art
Nowadays, particleboard, fiberboard, and the like as well as lumber, plywood, veneer, and combined materials are used as wood-based building materials, furniture materials, display materials, sound absorbing materials, and various handicraft materials. Also, rigid materials or foamed materials of synthetic resin, such as polystyrene, polyethylene, polyurethane, phenol resin, melamine resin, and urea resin are used as display materials, sound absorbing materials, and heat insulating materials and the like.
Such materials used to these usages above depend on wood source and petroleum source. Lumber and plywood are wood itself and have high material strength sand dimensional stability. The portion of wood, which having such characteristics, is small, so that a usage percentage or yield of wood becomes disadvantageously low.
While, particleboard and fiberboard are made by combining wood chips and fibers adding synthetic resin bond to the mixture, heat-pressing it to form plates. These boards are made by chips or fibers of wood, so it is said that wood source are usefully used. However, cellulose fibers of wood are cut finely to made such boards, so that they have shortcomings of dynamic or mechanical strength and dimensional stability of the boards.
Wood materials, such as lumber, plywood, particleboard, and fiberboard and the like, which have been used very much as building materials and the like, are respectively made of mainly natural wood. With recent exhaustion of wood source, the supply of wood seems to have a limit. Consequently, it will be impossible to completely satisfy high demand of wood in future, and price of wood will be raised very much.
Foamed materials of synthetic resin, such as polystyrene, polyethylene, polyurethane, and phenol resin and the like are light and have good workability and excellent heat insulation, so that they are widely used as a display material and heat insulation material. These resins depend on petroleum source, which has a limit, and therefore it is afraid that the source will be exhausted in near future.
In order to deal with such situation of the world, the inventors have filed Patent Applications of laminated materials and method for manufacturing the same using straight portions of lignocellulosic stalks of sorghum, corn, sugar cane, respectively which are reproduced every year and difficult even to abandon or abolish (Japanese Patent Application Laid-open Sho 63-107505, Japanese Patent Application Laid-open Hei 1-280538).
According to the method described in the former specification of Patent Application Laid-open Sho 63-107505, vegetable stalks of sorghum, corn, sugar cane are cut along their fiber directions, if necessary, core portions, are removed, the cut open stalks are pressed, a plurality of pressed stalks are arranged in parallel in order to form sheets of stalks, a well-known adhesive is applied on plural sheets, adhered sheets are laminated, and they are pressformed.
According to the method described in the latter specification of Patent Application Laid-open Hei 1-280538, sorghum stalks are pressed flat to make flat stalks, a plurality of flat stalks are arranged to form flat stalks layer, well-known adhesives are spread on the plural flat stalk layers, finally the layers are laminated and pressformed.
Laminated materials made by these methods are wood materials having any specific gravity, thickness, size and having a performance of excellent mechanical strength.
However, according to the former method, although a very high mechanical strength and a dimensional stability of the plate material can be obtained, it necessitates a number of steps including cutting step of the vegetable stalks, a core-removing step and a pressing step so as to produce a piece of laminated material of a predetermined thickness and also necessitates much volume of raw material of vegetable stalks, resulting in a problem of high manufacturing cost of the products.
According to the latter method, although the manufacturing cost is low, the product of laminated material has a lower mechanical strength than that of the laminated material produce by the former. Furthermore, when the laminated material is soaked and it contains water, the laminated material is disadvantageously swelled and thicken.